C:\>net start SwPrv
The MS Software Shadow Copy Provider service is starting.
The MS Software Shadow Copy Provider service was started successfully.
C:\>net start vss
The Volume Shadow Copy service is starting.
The Volume Shadow Copy service was started successfully.

If these reported errors, then your version of windows does not have these services. Does ntbackup still work for you, as I believe these services need to be running for ntbackup to operate correctly.